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Kernel: Implemented mutex priority inheritance.

Browse source 
Verified with a hwtest and implemented based on reverse engineering.

Thread A's priority will get bumped to the highest priority among all the threads that are waiting for a mutex that A holds.
Once A releases the mutex and ownership is transferred to B, A's priority will return to normal and B's priority will be bumped.
This commit is contained in:
Subv 2018-04-20 20:15:16 -05:00
parent a70ed9c8ae
commit 46572d027d
4 changed files with 94 additions and 10 deletions
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39
src/core/hle/kernel/mutex.cpp
View file

@ -18,13 +18,13 @@ namespace Kernel {
/// Returns the number of threads that are waiting for a mutex, and the highest priority one among
/// those.
static std::pair<SharedPtr<Thread>, u32> GetHighestPriorityMutexWaitingThread(VAddr mutex_addr) {
auto& thread_list = Core::System::GetInstance().Scheduler().GetThreadList();
static std::pair<SharedPtr<Thread>, u32> GetHighestPriorityMutexWaitingThread(
SharedPtr<Thread> current_thread, VAddr mutex_addr) {
SharedPtr<Thread> highest_priority_thread;
u32 num_waiters = 0;
for (auto& thread : thread_list) {
for (auto& thread : current_thread->wait_mutex_threads) {
if (thread->mutex_wait_address != mutex_addr)
continue;
@ -40,6 +40,21 @@ static std::pair<SharedPtr<Thread>, u32> GetHighestPriorityMutexWaitingThread(VA
return {highest_priority_thread, num_waiters};
}
/// Update the mutex owner field of all threads waiting on the mutex to point to the new owner.
static void TransferMutexOwnership(VAddr mutex_addr, SharedPtr<Thread> current_thread,
SharedPtr<Thread> new_owner) {
auto threads = current_thread->wait_mutex_threads;
for (auto& thread : threads) {
if (thread->mutex_wait_address != mutex_addr)
continue;
ASSERT(thread->lock_owner == current_thread);
current_thread->RemoveMutexWaiter(thread);
if (new_owner != thread)
new_owner->AddMutexWaiter(thread);
}
}
ResultCode Mutex::TryAcquire(VAddr address, Handle holding_thread_handle,
Handle requesting_thread_handle) {
// The mutex address must be 4-byte aligned
@ -65,11 +80,14 @@ ResultCode Mutex::TryAcquire(VAddr address, Handle holding_thread_handle,
return ERR_INVALID_HANDLE;
// Wait until the mutex is released
requesting_thread->mutex_wait_address = address;
requesting_thread->wait_handle = requesting_thread_handle;
GetCurrentThread()->mutex_wait_address = address;
GetCurrentThread()->wait_handle = requesting_thread_handle;
requesting_thread->status = THREADSTATUS_WAIT_MUTEX;
requesting_thread->wakeup_callback = nullptr;
GetCurrentThread()->status = THREADSTATUS_WAIT_MUTEX;
GetCurrentThread()->wakeup_callback = nullptr;
// Update the lock holder thread's priority to prevent priority inversion.
holding_thread->AddMutexWaiter(GetCurrentThread());
Core::System::GetInstance().PrepareReschedule();
@ -82,14 +100,18 @@ ResultCode Mutex::Release(VAddr address) {
return ResultCode(ErrorModule::Kernel, ErrCodes::MisalignedAddress);
}
auto [thread, num_waiters] = GetHighestPriorityMutexWaitingThread(address);
auto [thread, num_waiters] = GetHighestPriorityMutexWaitingThread(GetCurrentThread(), address);
// There are no more threads waiting for the mutex, release it completely.
if (thread == nullptr) {
ASSERT(GetCurrentThread()->wait_mutex_threads.empty());
Memory::Write32(address, 0);
return RESULT_SUCCESS;
}
// Transfer the ownership of the mutex from the previous owner to the new one.
TransferMutexOwnership(address, GetCurrentThread(), thread);
u32 mutex_value = thread->wait_handle;
if (num_waiters >= 2) {
@ -103,6 +125,7 @@ ResultCode Mutex::Release(VAddr address) {
ASSERT(thread->status == THREADSTATUS_WAIT_MUTEX);
thread->ResumeFromWait();
thread->lock_owner = nullptr;
thread->condvar_wait_address = 0;
thread->mutex_wait_address = 0;
thread->wait_handle = 0;